The principle behind the use of tubing within a pipe is well known. It consists of using an old gas-distributing pipe as a sleeve, through which is passed, for example by pulling it by means of a traction cable, a new distributing pipe having a diameter smaller than that of the old pipe.
This procedure avoids opening up a trench running the entire length of the site and offers major technical and economic advantages. The removal of only a small amount of earthwork over a short distance is required to free the pipe on which the work is to be done.
At these points, the old pipe, after having been freed, is cut and laid.
At the site of this cut, the pipe has a sharp angle and sometimes burrs, which risks damaging the new piping to be installed.
This is the reason protection must be provided for this new piping, which protection must be laid so as to provide support for the piping at the point of the cut by helping to center it and preventing the fill material from running into the old pipe being worked on.
At present, the known technique calls in particular for using a cuff to protect the new piping and for blocking, over a more or less long section of the pipe and at the point of the cut made, the free annular space between the new piping and the old pipe by means of a filling or packing material such as plaster, fast-drying cement, or polyurethane foam.
However, this approach is inconvenient and takes a long time to complete. In addition, it blocks the free, cut end of the old pipe only imperfectly; this blocking also holds rather poorly over time.
During the operation of pulling the new piping through the old pipe, the technique also calls for using temporary protection of the plank, roller, and gutter type, or pieces of flexible material, so as to guide and facilitate the sliding of the new piping into the old pipe.
However, as these methods are relatively disparate, they are poorly adapted in terms both of their ease of installation and of their effectiveness in guiding and protecting.